Is the Keyhole Garden Right for You?

By Rick Gibson

Cooperative Extension Agent, Agriculture

Pinal County, Arizona

If anyone has a keyhole garden, please let me know.  I am anxious to find out how they do here in our Arizona deserts.

Named for their distinctive shape, keyhole gardens are used commonly in water stressed areas of Africa to help families grow healthy vegetables.  Quoting the BBC, one report stated that three keyhole gardens have been known to support a family of ten with fresh vegetables all year long.  If true, it sure impresses me.

Here in the desert, we are always looking for new ways to grow fresh, tasty vegetables, cut down on the labor and save water.  From what I am reading, a keyhole garden might be just the ticket.  I haven’t yet tried one myself, but I am figuring someone out there has.  If you have a keyhole garden, or know someone who does, I would sure like to hear from you.

For those who may be unfamiliar with the concept, let me explain.  A keyhole garden is a raised bed structure, about six feet in diameter and about three feet high.  Some gardens are shorter and some are taller.  The round shape of the garden itself; a basket-type structure in the center of the bed where composting of kitchen wastes and other materials occurs; and a notch in the wall of the bed to allow easy access to the basket give a keyhole garden its name.  Viewed from above, the shape of the bed, basket and notch resemble an old fashioned key hole in a door.

The central basket might be a new concept for some.  It sits right in the middle of the garden and can either be round or square depending upon the materials from which it is constructed, or the whims of the builder.  Most baskets that I have studied seem to be about one foot in diameter.  Some are slightly larger.  In Africa, they are mostly made from tree branches and vines, all locally grown.  In America, some baskets have been constructed from branches, plastic netting or other materials.  No matter how it is constructed, it is the nutritional and water hub of the garden. 

It is into this central basket that vegetable kitchen wastes, lawn trimmings and other biodegradable plant materials are regularly added.  These materials breakdown over time through the composting process and provide essential nutrients for the garden plants.  The basket is also designed to receive extra water, generally from a hose or bucket.  In Africa, excess water from the kitchen or laundry is poured into the basket.  From there it distributes out through the garden. In America, a drip system is sometimes used to provide water in a timely manner. 

The garden itself is almost always six feet in diameter.  This is important because a smaller bed will not enough room to grow a good crop of vegetables.  A larger diameter would make it difficult to reach the innermost garden plants from the outer edge of the bed.  If the central basket is one foot in diameter and the total garden six, subtracting the one foot basket area, makes the total reach from any given point from the perimeter of the bed about two and one-half feet, an easy reach even for adults but a stretch for children.  The diameter of the garden should not be any more than six feet, especially if the garden is going to be a family project.

The notch in the bed extends far enough into the garden to allow access to the basket.  Access is needed to add composting materials and water to the garden through the basket.  I am not sure how the movement of nutrients and water from the basket to the plants will work under our hot climatic conditions.  This is where we need some local, practical experience.

In Africa, the composting materials release nitrogen and other nutrients which are made available to the plants, especially when the only source of water comes from the basket.  Dissolved in water, the nutrients move through the garden bed to a point where the plant roots can pick them up.  This is logical because of the way the interior of the garden is structured. Let’s talk about that next.

The garden itself is constructed in such a manner that water drains down hill away from the basket and towards the plants. Some reports say that the roots of plants also tend to grow towards the basket and water source. This efficiency helps reduce the water requirements of the garden.  Reports out of Texas indicate that during the recent serious drought, they had to add a drip irrigation system to keep the plants healthy.  Even with a drip irrigation system, the keyhole garden seems to be a low water use garden system.

If you would like to build your own keyhole garden, here is what you do.  First, find a location in a sunny area and measure out a six-foot diameter circle.  Scribe a circle so that you can see the outline.  Next, notch out a section of the circle wide enough to access the basket that will be placed in the center of the garden.  The amount of space needed for this access will be dependent upon the size of the person that will need to squeeze in to do the tasks and the amount of space needed to grow garden plants.  Remember that every square inch of space you allocate for access will be that much space lost to food production.

The walls of the garden are constructed of bricks, paving stones or other firm materials that will keep the garden soil inside the garden.  You can make it as tall as you wish, but it probably should not be made taller than your waist is high.  That makes it easy to work the beds.

Once you have laid the first couple of layers of stone or brick, set your basket or cylinder into place and fill it full of plant material. This will be your compost pile.  Mix in a little regular soil and soak the material to start the composting process.

Outside the basket, and in the garden area, lay down a layer of stiff branches or dried weeds and cover this layer with ordinary cardboard.  Now this is important.  You want the layers to slope away from the basket so that water and nutrients drain away from the basket.  The slope does not need to be too steep; just enough to let the water run down hill.  On top of the cardboard, place a three or four inches of regular soil, followed by a layer of plant material, followed by more soil.  Alternate the layers until the top layer of soil is up to the desired grade.  Add a drip system if you like, or experiment to see if the African drainage model works.  When all is prepared, plant your garden.

I suspect that there will be many questions.  If you want to learn more, and have a computer with internet service, simply do a web search for “keyhole garden.”  I learned a lot that way.      

A keyhole garden is unique; not only in its shape, but also in its intent and productivity.  The objective is to recycle and convert waste materials into productive garden soil and save water in the process.  If you are short of space in your yard, don’t really want to bend over while working in your garden and want to save water while growing healthy vegetables for home use, consider building a keyhole garden.

If you have questions, you can reach one of the Master Gardeners at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande.  The telephone is (520) 836-5221, extension 204.  The author’s email address is gibsonrd@ag.arizona.edu.

The University of Arizona is an equal opportunity, affirmative action institution.  The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.

Rick Gibson

Extension Agent, Agriculture

University of Arizona Cooperative Extension

820 E. Cottonwood Lane, Building C

Casa Grande, Arizona 85222

Voice:  (520) 836-5221

Fax:     (520) 836-1750

Cell:     (520) 705-1141

email:   gibsonrd@ag.arizona.edu